1. Field of the Invention
The present invention relates to an exchange coupling film utilizing exchange coupling which acts between a ferromagnetic layer and an antiferromagnetic layer, a magneto-resistance effect device having the exchange coupling film, and a reproducing magnetic head and a magnetic random access memory which use the magneto-resistance effect device.
2. Description of the Related Art
A so-called spin valve type of magneto-resistance effect device is used for a magnetic random access memory (MRAM) which is notable as a reproducing magnetic head and a nonvolatile memory of a hard disk drive (HDD) apparatus corresponding to high magnetic recording density. A basic structure of the spin valve type of magneto-resistance effect device is a multilayer in which a ferromagnetic layer, a nonmagnetic material layer, the ferromagnetic layer, and an antiferromagnetic layer are formed in the order or in reverse. At this point, a magnetic moment of the ferromagnetic layer adjoining the antiferromagnetic layer is fixed by exchange coupling (it is also referred to as exchange bias) which acts between the antiferromagnetic layer and the ferromagnetic layer adjoining the antiferromagnetic layer so as not to rotate the magnetic moment to an external magnetic field, so that the ferromagnetic layer is referred to as a fixing layer or a pinning layer. Generally a multilayered film including the ferromagnetic layer and the antiferromagnetic layer is referred to as an exchange coupling film or an exchange bias film. The magnetic moment of the other ferromagnetic layer isolated from the pinning layer through the nonmagnetic material layer can be rotate responsive to the external magnetic field, so that the ferromagnetic layer is referred to as a free layer.
The spin valve type of magneto-resistance effect device is divided into two kinds by difference in the nonmagnetic material layer: (1) A giant magneto-resistance effect (GMR) device in which the nonmagnetic material layer includes nonmagnetic metal such as Cu and (2) A tunnel magneto-resistance effect (TMR) device in which the nonmagnetic material layer includes an insulating layer (tunnel barrier layer) such as aluminum oxide (AlOX). The TMR device is also referred to as a ferromagnetic tunnel junction device. In any of the devices, by utilizing a phenomenon that a relative angle defined by the magnetic moment of the free layer and that of the pinning layer changes as conductance of the device changes, information of a magnetic recording medium is read in case of a reproducing magnetic head of the HDD apparatus and information of stored bits is read in case of the MRAM. With respect to write, the magnetic moment of a recording bit in the magnetic recording medium is reversed by using a fringing field from a recording magnetic head in case of the HDD apparatus, the magnetic moment of the free layer in the device is reversed by a resultant magnetic field which current flown through a bit line and a word line forms in case of the MRAM.
The conductance of the device is dependent on cos xcex8, where an angle defined by the magnetic moment of the free layer and that of the pinning layer is xcex8, the conductance becomes a maximum in case that the both magnetic moments are parallel to each other (xcex8=0xc2x0), the conductance becomes a minimum in case that the both magnetic moments are antiparallel to each other (xcex8=180xc2x0).
In the GMR device and the TMR device, the GMR device differs completely from the TMR device in physical origin, however it is the same to utilize an effect that the conductance of the device changes corresponding to a change in the relative angle (xcex8) of the magnetic moments of the both magnetic layers, namely the magneto-resistance effect. That is to say, magnetic resistance of the GMR device is derived from a difference in scattering length between an electron having spin-up and an electron having spin-down depending on the angle defined by the magnetic moment of the free layer and that of the pinning layer, on the other hand, the magnetic resistance of the TMR device is derived from a difference in tunnel probability between an electron having spin-up and an electron having spin-down depending on the angle.
FIG. 1 is a graph showing hysteresis curves of dependence of magnetization of the spin valve type of magneto-resistance effect device on a magnetic field (M-H curve) and dependence of resistance (inverse number of the conductance) on the magnetic field (R-H curve), where transverse axes are magnetic field strength and longitudinal axes are the magnetization and the resistance. The sharp hysteresis near the zero magnetic field corresponds to a magnetic rotation of the free layer, and the hysteresis appeared in the high magnetic field corresponds to the magnetic rotation of the pinning layer. The shift in the hysteresis of the pinning layer is derived from the exchange coupling (it is also referred to as the exchange bias) acting an interlayer between the pinning layer (ferromagnetic layer) and the antiferromagnetic layer adjoining the pinning layer (hereinafter referred to as ferromagnetic-layer/antiferromagnetic-layer interlayer), shift quantity Hex of the hysteresis of the pinning layer from the zero magnetic field is referred to as an exchange coupling magnetic field (it is also referred to as exchange bias magnetic field). A magnetization direction of the free layer is antiparallel to the magnetization direction of the pinning layer within an area between the hysteresis of the free layer and that of the pinning layer, the resistance of the device becomes larger and the conductance of the device becomes smaller within the area.
In the both spin valve type of magneto-resistance effect devices of the GMR and the TMR, it is necessary that the magnetic moment of the pinning layer is fixed in one direction for stable operation of the device, and it is necessary that the strong exchange coupling in the ferromagnetic-layer/antiferromagnetic-layer interlayer is generated and the hysteresis of the free layer is sufficiently separated from the hysteresis of the pinning layer, namely the area where the magnetic moment of the free layer is antiparallel to that of the pinning layer is extended. For the purpose, the exchange coupling magnetic field Hex must be increased while expansion of the hysteresis of the pinning layer, namely coercive force Hcp shown in FIG. 1 is decreased.
The exchange coupling energy J acting the ferromagnetic-layer/antiferromagnetic-layer interlayer is given as follows:
J=Hexxc3x97Msxc3x97txe2x80x83xe2x80x83(FORMULA 1)
where the exchange coupling magnetic field is Hex, saturation magnetization of the ferromagnetic layer is Ms, and a film thickness of the ferromagnetic layer is t.
It is generally recognized that the exchange coupling energy J is decided by a combination of the antiferromagnetic material and the ferromagnetic material. As shown obviously in the formula 1, the exchange coupling magnetic field Hex increases as the film thickness of the ferromagnetic layer t decreases when the exchange coupling energy J is constant. However the exchange coupling magnetic field Hex may be increased seemingly by decreasing film thickness of the pinning layer, it is limited that the exchange coupling magnetic field Hex is increased only by decreasing film thickness of the pinning layer because the coercive force Hcp is tend to increase with decreasing film thickness of the ferromagnetic layer t. When an oxide material typified by NiO or an ordered alloy typified by PtMn is used as the antiferromagnetic material, the coercive force of the pinning layer becomes larger than the exchange coupling magnetic field Hex, which causes a problem in device operation. Accordingly, in order to increase the exchange coupling magnetic field Hex, it is necessary that firstly the exchange coupling energy is increased, secondly the film thickness of the pinning layer is decreased within a range where operation of the magneto-resistance device is not damaged, and thirdly the coercive force of the hysteresis of the pinning layer is decreased within a range where the exchange coupling magnetic field is not largely decreased. For this reason, various materials and multilayered configurations have been proposed as described below in detail.
A disordered alloy type of antiferromagnetic material having face-centered cubic structure typified by IrMn and an ordered alloy type of antiferromagnetic material of a CuAuxe2x80x94I type (L10 type) having face-centered tetragonal structure typified by PtMn are known as the antiferromagnetic material having high resistance to a manufacturing process of the magnetic head and the MRAM and the large exchange coupling energy. For example, an exchange coupling film utilizing the antiferromagnetic material made of an IrMn alloy and a magneto-resistance effect device using the exchange coupling film are disclosed in Japanese Patent Application Laid-Open No. 148132/1997 and Japanese Patent Application Laid-Open No. 2001-102215. Magneto-resistance effect devices having the pinning layer of the exchange coupling film utilizing the ordered alloy type of antiferromagnetic material made of PdMn and PtMn are disclosed in Japanese Patent Application Laid-Open No. 81915/1997 and Japanese Patent Application Laid-Open No. 147325/1997 respectively. Another magneto-resistance effect device having the pinning layer of the exchange coupling film utilizing the ordered alloy type of antiferromagnetic material made of PdPtMnCr is disclosed in Japanese Patent Application Laid-Open No. 2000-251226. Furthermore, magneto-resistance effect devices having the pinning layer of the exchange coupling film utilizing the ordered alloy type of antiferromagnetic material made of NiMn are disclosed in Japanese Patent Application Laid-Open No. 60336/1994 and Japanese Patent Application Laid-Open No. 63021/1997.
A technique that the exchange coupling is increased by building up the antiferromagnetic layers has been also developed. For example, a spin valve type of magneto-resistance sensor having the exchange coupling film formed by building up a plurality of antiferromagnetic layers with variation of elements or composition of an alloy is disclosed in Japanese Patent Application Laid-Open No. 2000-132814. A magneto-resistance effect device having the exchange coupling film formed by multilayered films of a disordered alloy type of antiferromagnetic layer and an ordered alloy type of antiferromagnetic layer is disclosed in Japanese Patent Application Laid-Open No. 175919/1999. An exchange coupling film, in which the antiferromagnetic layer is consisted of two portions, namely the portion near the pinning layer is mainly consisted of a xcex3-Mn phase and the other portion is mainly consisted of an xcex1-Mn phase, is disclosed in Japanese Patent Application Laid-Open No. 111522/1999.
A technique that the exchange coupling is increased by controlling a crystal orientation of the antiferromagnetic layer has been also disclosed. For example, an exchange coupling film, in which the large exchange coupling is obtained by improving the crystal orientation of an IrMn layer in such a manner as to form a controlling layer of the crystal orientation, a controlling layer of crystal structure, and a lattice controlling layer beneath the IrMn layer, is disclosed in Japanese Patent Application Laid-Open No. 208215/1998. Another exchange coupling film characterized in that the antiferromagnetic layer of the CuAuxe2x80x94I type of ordered alloy is formed on a promoting layer for antiferromagnetism and the antiferromagnetic layer has the (110) orientation is disclosed in Japanese Patent Application Laid-Open No. 2000-22239. Another exchange coupling film having the antiferromagnetic layer of epitaxial grown NiMn is disclosed in Japanese Patent Application Laid-Open No. 275723/1998.
A technique that the large exchange coupling is given by controlling grain structure of the antiferromagnetic layer or interfacial structure of the antiferromagnetic layer and the ferromagnetic layer has been also known. For example, an exchange coupling film, which has an average grain diameter of the antiferromagnetic layer not smaller than 5 nm and the uniform crystal orientation of the surface in such a manner as to form by using an alloy target having oxygen content of not more than 1 wt %, is disclosed in Japanese Patent Application Laid-Open No. 284321/1998. Another exchange coupling film having the antiferromagnetic layer, in which a full width at half maximum of a rocking curve of a (111) peak by X-ray diffraction is not more than 100 and the average grain diameter is in a range from 3 to 50 nm, is disclosed in Japanese Patent Application Laid-Open No. 2000-68569. Another exchange coupling film characterized in that the interfacial structure of the ordered alloy type of antiferromagnetic layer and the ferromagnetic layer is a disconformable state, namely the ferromagnetic layer is (111) orientation and the antiferromagnetic layer is not oriented, is disclosed in Japanese Patent Application Laid-Open No. 191647/1999.
Furthermore, however the orientation of the antiferromagnetic layer is not always increased, in a exchange coupling film having laminated structure of substrate layer (seed layer), antiferromagnetic layer, and ferromagnetic layer (pinning layer), it is known that the exchange coupling energy and the exchange coupling magnetic field vary by a kind and a thickness of the substrate layer (seed layer).
In case that a multilayer film is built up in the order of a layer made of a component X and having a film thickness of x nm, a layer made of a component Y and having a film thickness of y nm, and a layer made of a component Z and having a film thickness of z nm, the multilayer film is represented as xe2x80x9cX layer (x nm)/Y layer (y nm)/Z layer (z nm)xe2x80x9d. Each of x, y, and z is a numeral showing a film thickness. Further, in case that the film thickness is not specified, the multilayer film is represented as xe2x80x9cX layer/Y layer/Z layerxe2x80x9d.
In the Proceedings of the 24th Annual Conference (2000) page 409 of xe2x80x9cThe Magnetics Society of Japanxe2x80x9d, in a GMR film provided with a configuration of Ta layer (5 nm)/seed layer (appropriate thickness)/IrMn layer (6.8 nm)/CoFe layer (2 nm)/Cu layer (2.5 nm)/CoFe layer (2 nm)/capping layer (appropriate thickness), which formed on the substrate, the exchange coupling magnetic field Hex is 1030 Oe in case that the seed layer is a Cu layer (1 nm), the exchange coupling magnetic field Hex is 1270 Oe in case that the seed layer is a double layer of NiFe layer (1 nm)/Cu layer (1 nm), and the exchange coupling magnetic field Hex is 1290 Oe in case that the seed layer is a double layer of CoFe layer (1 nm)/Cu layer (1 nm). When these values of the exchange coupling magnetic field Hex are converted into the exchange coupling energy, the converted values are approximately equal to the value (exchange coupling energy J=0.36xc3x9710xe2x88x927J/cm3) of the film made of the ordered alloy type of antiferromagnetic layer.
The above-described techniques are based on a method that the exchange coupling is increased by controlling a thin film structure (crystal orientation and grain structure) of the antiferromagnetic layer. On the other hand, since the exchange coupling acts the interface between the antiferromagnetic layer and the ferromagnetic layer, there is another technique that the exchange coupling is increased by focusing on the interfacial in a manner that an interface control layer is provided between the antiferromagnetic layer and the ferromagnetic layer to increase coherence of the interface between the antiferromagnetic layer and the ferromagnetic layer.
For example, there is a technique that the exchange coupling is increased in a manner that the interface control layer being coherent to both crystal lattices of the antiferromagnetic layer and the ferromagnetic layer is provided between the antiferromagnetic layer and the ferromagnetic layer to secure crystalline structure of the both layers. An exchange coupling film having a plasma treatment layer in which several atomic layers in at least one of a surface of the ferromagnetic layer (pinning layer) and an initial growth layer of the antiferromagnetic layer is treated by plasma treatment of an argon ion is disclosed in Japanese Patent Application Laid-Open No. 2000-268330.
There is also an interface control layer whose purpose of formation is increment of separation of the hysteresis of the free layer in the spin valve type of magneto-resistance effect device from the hysteresis of the pinning layer by reducing the coercive force of the hysteresis of the pinning layer without influence on the exchange coupling magnetic field rather than increment of the exchange coupling. However there is a problem that the coercive force of the pinning layer is large and an area where the magnetic moment of the free layer is antiparallel to the magnetic moment of the pinning layer is narrow, a technique which reduces the coercive force of the pinning layer by inserting the interface control layer made of the nonmagnetic metal or the oxide material including Cr or Mn with the film thickness of 0.3 to 2 nm between the antiferromagnetic layer of NiO and the pinning layer (ferromagnetic layer) is described in Japanese Patent No. 2850866.
Especially, in the exchange coupling film made of the antiferromagnetic layer of the ordered alloy, though the exchange coupling magnetic field is relatively large, the coercive force of the pinning layer becomes considerably large, which causes the hysteresis of the free layer and the hysteresis of the pinning layer to be separated insufficiently in case of the spin valve type of magneto-resistance effect device. As a result, there is a problem that good device operation can not be realized. In such cases, it is necessary that the coercive force of the pinning layer is reduced within a range where the exchange coupling magnetic field is not extremely reduced. From a view point of the reduction of the coercive force of the pinning layer, it is known that a multilayered pinning layer is effective. Concretely the pinning layer is constituted by not lower than two ferromagnetic layers, the exchange coupling of the antiferromagnetic layer is shared by the ferromagnetic layer being contact with the antiferromagnetic layer, the low coercive force or a role except the exchange coupling such as resistance to heat treatment is shared by the ferromagnetic layer except the ferromagnetic layer being contact with the antiferromagnetic layer. Accordingly, it is found that the relatively large exchange coupling magnetic field and the small coercive force of the pinning layer can be compatible by the multilayered pinning layer, however it is difficult to achieve in the single pinning layer.
For example, it is described in Japanese Patent Application Laid-Open No. 2000-315305 that, in a spin valve sensor utilizing the exchange coupling film consisted of the antiferromagnetic layer and the pinning layer of the antiferromagnetic coupling (AFC) film of CoFe layer/Ru layer/CoFe layer/Ru layer/CoFe layer, the coercive force of the AFC film can be small by providing a double-layered interlayer made of CoFe and NiFe between the antiferromagnetic layer and the AFC film. The pinning layer utilizing the AFC film can obtain the larger exchange coupling magnetic field compared with the single pinning layer. This is because a first ferromagnetic layer of the AFC film is combined antiferromagnetically with a second ferromagnetic layer of the AFC film through a spacer layer such as Ru, which causes the magnetic moment of the whole AFC film to be equal to a difference between the magnetic moment of the first ferromagnetic material and the magnetic moment of the second ferromagnetic material. That is to say, the magnetic moment of the whole AFC film is smaller than that of the single ferromagnetic layer and the exchange coupling magnetic field Hex is inversely relate to the saturation magnetization Ms according to the formula 1, which allows the exchange coupling magnetic field of the AFC film to be increased. The spin valve sensor utilizing the AFC film as the pinning layer is described in U.S. Pat. No. 5,465,185.
There are particularly two problems of manufacturing as described below for using the AFC film as the pinning layer, however the above-described AFC film has an advantage of being capable of increasing the exchange coupling magnetic field. The first problem is that sufficiently large antiferromagnetic coupling needs to act between two magnetic material layers, so that the film thickness of the spacer layer requires strict control. The second problem is that, as described in Japanese Patent Application Laid-Open No. 2000-315305, it is necessary to form the pinning layer by the AFC film and another ferromagnetic layer in order to reduce the coercive force of the AFC film, which results in increment of the number of necessary targets forming the AFC film and enlargement of a manufacturing apparatus. From a view point of manufacturing cost of film formation, it is desirable that the AFC film is not used for the pinning layer as much as possible.
It is disclosed in Japanese Patent Application Laid-Open No. 232617/1999 that, in a spin valve type of magneto-resistance effect device having a configuration of first ferromagnetic layer (free layer)/nonmagnetic layer/second ferromagnetic layer (pinning layer)/antiferromagnetic layer, the second ferromagnetic layer (pinning layer) is a multilayer consisted of at least two ferromagnetic layers, the ferromagnetic layer of a side being in contact with the antiferromagnetic layer obtains the high exchange coupling energy at an interface between the antiferromagnetic layer and the ferromagnetic layer, and the ferromagnetic material has the small saturation magnetization in the ferromagnetic layer of a side being out of contact with the antiferromagnetic layer. It is described that the high exchange coupling magnetic field can be compatible with the small coercive force of the pinning layer by the pinning layer such as the configuration. It is also described that thermal stability is obtained in a manner that a ferromagnetic material being difficult to diffuse mutually into the nonmagnetic layer is used as the ferromagnetic material of the side being in contact with the nonmagnetic layer. In this technique, a material consisted of the ferromagnetic layer being contact with the antiferromagnetic layer depends on the antiferromagnetic material. For example, it is disclosed that, in case of the antiferromagnetic material of the ordered alloy represented by PtMn, the antiferromagnetic layer is formed by Co or CoFe alloy having the film thickness of at least 0.5 nm and NiFe is suitable for the ferromagnetic material having the small saturation magnetization.
However, in the technique disclosed in Japanese Patent Application Laid-Open No. 232617/1999, the second ferromagnetic layer (pinning layer) is consisted of at least two ferromagnetic layers, one of the two layers uses the ferromagnetic layer obtaining the large exchange coupling energy, and the other layer uses the ferromagnetic layer having the small saturation magnetization, when at least two ferromagnetic layers are deposited, the obtained characteristics as a whole become average characteristics of each layer, which causes remarkable performance not to be obtained.
An exchange coupling film consisted of the antiferromagnetic layer of an IrMn alloy and the ferromagnetic layer (pinning layer), in which the ferromagnetic layer (pinning layer) has multilayered structure of a Co or Co alloy layer and a NiFe alloy layer, the IrMn alloy layer is in contact with the Co or Co alloy layer, and a proportion of the thickness of the Co or Co alloy layer is 10 to 40% of the whole thickness of the pinning layer, is disclosed in Japanese Patent Application Laid-Open No. 188229/1998.
In the GMR device having the pinning layer of the multilayered structure consisted of two ferromagnetic layers, there is a case that the ferromagnetic layer of the nonmagnetic layer side has function as an MR enhanced layer in order not to increase the exchange coupling magnetic field or reduce the coercive force of the pinning layer, but in order to increase the magneto-resistance effect namely increase a ratio of change of the magneto-resistance. For example, it is disclosed in Japanese Patent Application Laid-Open No. 154311/1998 that a GMR device comprises the ferromagnetic layer being in contact with the antiferromagnetic layer using a crystalline ferromagnetic layer of a single metal, an alloy or a multilayered film made of Fe, Ni and/or Co and the MR enhanced ferromagnetic layer of the nonmagnetic layer side using an amorphous ferromagnetic layer such as CoFeB.
There is also multilayer structure consisted of at least two pinning layers of the ferromagnetic layer in order to improve resistance to heat treatment. In a ferromagnetic tunnel junction (TMR) device disclosed in Japanese Patent Application Laid-Open No. 2001-68757, the antiferromagnetic layer is made of a manganese ordered alloy, the ferromagnetic layer exchange-biased by the antiferromagnetic layer is constituted by the multilayer film of at least two layers, the ferromagnetic layer being in contact with the antiferromagnetic layer is made of a single cobalt metal, a cobalt alloy, or a cobalt compound, and the ferromagnetic layer being in contact with a tunnel barrier is made of a single nickel metal, a nickel alloy, or a nickel compound. This permits deterioration of device characteristics by heat treatment to be suppressed, even though the heat treatment which is needed during formation of the antiferromagnetic layer by the manganese ordered alloy is performed for hours at a higher temperature.
As described above, in the spin valve type of magneto-resistance effect device, the larger exchange coupling magnetic field and the exchange coupling film giving the smaller coercive force of the pinning layer are always required so as to improve operating stability and reliability of the device. Various techniques have been proposed in order to increase the exchange coupling magnetic field which acts between the pinning layer of the ferromagnetic layer and the antiferromagnetic layer and to reduce the coercive force of the pinning layer of the ferromagnetic layer.
The first technique is a method such that the exchange coupling is increased by controlling composition, a kind, or crystal structure of component elements constituting the antiferromagnetic layer. The techniques include a method controlling the thin film structure of the antiferromagnetic layer, namely the orientation and the crystal grain structure of the antiferromagnetic layer. Alloys including a platinum group (Pt, Pd, Ir, and Rh) and Mn are mainly used as the antiferromagnetic material having the chemical and thermal resistance to a manufacturing process of the magnetic head and MRAM and being capable of giving the exchange coupling magnetic field to at least a certain extent. Typically, it is an IrMn disordered alloy or a PtMn ordered alloy.
The second technique is a method such that, focusing on the interface between the ferromagnetic layer of the pinning layer and the antiferromagnetic layer, the exchange coupling is increased by providing the interface control layer between the ferromagnetic layer and the antiferromagnetic layer.
The third technique is a method such that the coercive force of the pinning layer is reduced without reducing the exchange coupling magnetic field remarkably in a manner that one of the ferromagnetic layer being in contact with the antiferromagnetic material has function of the exchange coupling with the antiferromagnetic material and the other ferromagnetic layer has function of the low coercive force with the ferromagnetic layer of the pinning layer as the multilayer structure including at least two ferromagnetic layer.
However, there are problems described below in the above described conventional techniques. It is difficult that the larger exchange coupling magnetic field and the smaller coercive force of the pinning layer are simultaneously achieved even in the exchange coupling film using the antiferromagnetic layer as described above. The coercive force of the pinning layer is small but the exchange coupling magnetic field is small in case of the exchange coupling film using the antiferromagnetic layer of the disordered alloy. On the other hand, the exchange coupling magnetic field is large but the coercive force of the pinning layer is also large considerably in case of the exchange coupling film using the antiferromagnetic layer of the ordered alloy. Accordingly, in order to improve the operating stability and the reliability of the spin valve type of magneto-resistance effect device used for the magnetic head and the MRAM, it is necessary that the exchange coupling field increases the exchange coupling magnetic field for the exchange coupling film using the antiferromagnetic layer of the disordered alloy and the exchange coupling film reduces the coercive force of the pinning layer for the exchange coupling film using the antiferromagnetic layer of the ordered alloy.
In the method that the ferromagnetic layer of the pinning layer is formed by at least two ferromagnetic layers, when the antiferromagnetic layer is made of the antiferromagnetic material including the ordered alloy of the L10 type (CuAuxe2x80x94I type) of face-centered cubic structure such as a PtMn alloy, a PdMn alloy, and a NiMn alloy, there is a problem which effect of the double-layered film is small, because it is not possible to reduce the coercive force of the pinning layer by the multilayered film of the pinning layer even though the exchange coupling energy can be increased somewhat compared with the single layer film of the pinning layer. As described above, sufficient performance of the spin valve type of magneto-resistance effect device can not be obtained in any conventional techniques.
It is an object of the present invention to provide an exchange coupling film, using an antiferromagnetic layer made of a disordered alloy, which can obtain larger exchange coupling energy than that of the exchange coupling film using an antiferromagnetic material made of an ordered alloy. The object of the present invention is achieved by solving a problem of the conventional exchange coupling film using the antiferromagnetic layer made of the disordered alloy such that coercive force of a pinning layer is small but the exchange coupling magnetic field is also small, and realizing the larger exchange coupling magnetic field with the small coercive force of the pinning layer maintained. It is an object of the present invention to provide a spin valve type of magneto-resistance effect device, which is provided with the exchange coupling film having such larger exchange coupling energy and has high operating stability and reliability, and a magneto-resistance sensor of a reproducing magnetic head and a magnetic random access memory which utilize the spin valve type of magneto-resistance effect device.
An exchange coupling film according to the invention comprises an antiferromagnetic layer formed of a disordered alloy, an exchange coupling giving layer formed of a ferromagnetic material selected from the group consisting of Co and CoFe alloy having face-centered cubic structure, being in contact with the antiferromagnetic layer, and giving exchange coupling at an interface between the antiferromagnetic layer and the exchange coupling giving layer, and an exchange coupling enhancement layer formed of a ferromagnetic material selected from the group consisting of Fe and CoFe alloy having body-centered cubic structure and provided on the exchange coupling giving layer so that the exchange coupling giving layer is sandwiched between the antiferromagnetic layer and the exchange coupling enhancement layer, the exchange coupling enhancement layer amplifying the exchange coupling by the exchange coupling giving layer.
According to the invention, in an exchange coupling film including the ferromagnetic layer of a pinning layer (fixing layer) and the antiferromagnetic layer, a double-layered film including the exchange coupling giving layer and the exchange coupling enhancement layer is used as the pinning layer and an optimum combination among the antiferromagnetic layer, the exchange coupling giving layer, and the exchange coupling enhancement layer is selected, which permits the exchange coupling to be increased comparing with the pinning layer of a single layer. That is to say, the exchange coupling can be remarkably increased in a manner that the antiferromagnetic layer is formed by the antiferromagnetic material including the disordered alloy, the exchange coupling giving layer is formed by the ferromagnetic material made of Co or the CoFe alloy having the face-centered cubic structure, and the exchange coupling enhancement layer is formed by the ferromagnetic material made of Fe or the CoFe alloy having the body-centered cubic structure.
Another exchange coupling film according to the invention comprises an antiferromagnetic layer formed of a disordered alloy, an exchange coupling giving layer formed of an amorphous ferromagnetic material made of CoFe, being in contact with the antiferromagnetic layer, and giving exchange coupling at an interface between the antiferromagnetic layer and the exchange coupling giving layer, and an exchange coupling enhancement layer formed of a ferromagnetic material selected from the group consisting of Fe and CoFe alloy having body-centered cubic structure and provided on the exchange coupling giving layer so that the exchange coupling giving layer is sandwiched between the antiferromagnetic layer and the exchange coupling enhancement layer, the exchange coupling enhancement layer amplifying the exchange coupling by the exchange coupling giving layer.
In the invention, the exchange coupling can be remarkably increased in a manner that the antiferromagnetic layer is formed by the antiferromagnetic material including the disordered alloy, the exchange coupling giving layer is formed by the amorphous ferromagnetic material made of CoFe, and the exchange coupling enhancement layer is formed by the ferromagnetic material made of Fe or the CoFe alloy having the body-centered cubic structure.
An IrMn alloy may be used as the disordered alloy. An FeMn alloy, the IrMn alloy, and a RhMn alloy of the face-centered cubic structure are known as the antiferromagnetic material made of the disordered alloy, particularly in case that the antiferromagnetic layer is made of the IrMn alloy, the most remarkable effect, namely extremely large exchange coupling magnetic field can be obtained.
A magneto-resistance effect device according to the invention comprises a magnetization fixing layer in which a direction of magnetic moment is fixed, a free layer in which the direction of the magnetic moment is rotated by an external magnetic field, and a nonmagnetic layer provided between the magnetization fixing layer and the free layer. The magnetization fixing layer comprises an antiferromagnetic layer formed of a disordered alloy, an exchange coupling giving layer formed of a ferromagnetic material selected from the group consisting of Co and CoFe alloy having face-centered cubic structure, being in contact with the antiferromagnetic layer, and giving exchange coupling at an interface between the antiferromagnetic layer and the exchange coupling giving layer, and an exchange coupling enhancement layer formed of a ferromagnetic material selected from the group consisting of Fe and CoFe alloy having body-centered cubic structure and provided on the exchange coupling giving layer so that the exchange coupling giving layer is sandwiched between the antiferromagnetic layer and the exchange coupling enhancement layer, the exchange coupling enhancement layer amplifying the exchange coupling by the exchange coupling giving layer.
In the invention, since an antiparallel state between the magnetic moment of a pinning layer and the magnetic moment of the free layer can be realized in a wide range of the magnetic field, operating stability of the magneto-resistance effect device can be achieved, which results in improvement of reliability. There are a giant magnetic resistance (GMR) type of magneto-resistance effect device whose nonmagnetic layer is made of Cu and a tunneling magnetic resistance (TMR) type of magneto-resistance effect device whose nonmagnetic layer is formed by a tunnel barrier insulator in the magneto-resistance effect devices, the same effect can be obtained in either type. Aluminum oxide (AiOx) and aluminum nitride (AlN) are used as the tunnel barrier insulator.
Another magneto-resistance effect device according to the invention comprises a magnetization fixing layer in which a direction of magnetic moment is fixed, a free layer in which the direction of the magnetic moment is rotated by an external magnetic field, and a nonmagnetic layer provided between the magnetization fixing layer and the free layer. The magnetization fixing layer comprises an antiferromagnetic layer formed of a disordered alloy, an exchange coupling giving layer formed of an amorphous ferromagnetic material made of CoFe, being in contact with the antiferromagnetic layer, and giving exchange coupling at an interface between the antiferromagnetic layer and the exchange coupling giving layer, and an exchange coupling enhancement layer formed of a ferromagnetic material selected from the group consisting of Fe and CoFe alloy having body-centered cubic structure and provided on the exchange coupling giving layer so that the exchange coupling giving layer is sandwiched between the antiferromagnetic layer and the exchange coupling enhancement layer, the exchange coupling enhancement layer amplifying the exchange coupling by the exchange coupling giving layer.
A magnetic head according to the invention is a magnetic head with the magneto-resistance effect device. Because an antiparallel state between the magnetic moment of a pinning layer and that of the free layer can be realized in a wide range of the magnetic field by using an exchange coupling film as a magnetization fixing layer, operating stability of the magneto-resistance effect device and reliability can be improved. Consequently, the stability and the reliability of the magnetic head can be improved. The same effect can be obtained in both magnetic heads of the magnetic head including the giant magnetic resistance (GMR) type of magneto-resistance effect device whose nonmagnetic layer is made of Cu and the magnetic head including the tunneling magnetic resistance (TMR) type of magneto-resistance effect device whose nonmagnetic layer is formed by the tunnel barrier insulator.
A magnetic random access memory according to the invention is a magnetic random access memory with the magneto-resistance effect device. Because an antiparallel state between the magnetic moment of a pinning layer and that of the free layer can be realized in a wide range of the magnetic field by using an exchange coupling film as a magnetization fixing layer, operating stability of the device and reliability can be improved. Consequently, the stability and the reliability of the magnetic random access memory (MRAM) can be improved. The same effect can be obtained in both random access memories of the random access memory including the giant magnetic resistance (GMR) type of magneto-resistance effect device whose nonmagnetic layer is made of Cu and the magnetic random access memory including the tunneling magnetic resistance (TMR) type of magneto-resistance effect device whose nonmagnetic layer is formed by the tunnel barrier insulator.
As described above in detail, according to the invention, the larger exchange coupling magnetic field is achieved with the small coercive force of the pinning layer maintained, which permits the exchange coupling film having the large exchange coupling energy to be obtained in the exchange coupling film using the antiferromagnetic layer including the disordered alloy.